1. Field of the Invention
The present invention relates to a delivery valve to deliver compressed refrigerant from a scroll compressor incorporated into a refrigerator or an air conditioner.
2. Description of the Prior Art
FIG. 5 is a sectional view of a prior art scroll compressor disclosed in, for example, Japanese Patent Laid-open (Kokai) No. Hei 2-163486 and FIG. 6 is an enlarged sectional view of a portion of FIG. 5.
This prior art scroll compressor has a stationary scroll plate 1 and a revolving scroll plate 2. The stationary scroll plate 1 is fastened closely to the surface of an upper wall of a closed vessel 10 so as to partition the interior of the closed vessel 10 into a high-pressure chamber VH and a low-pressure chamber VL.
The stationary scroll plate 1 has a stationary disk 1a, a circumferential annular wall 1b having the shape of a skirt and formed integrally with the stationary disk 1a, and a scroll wrap 1c protruding from the lower surface of the stationary disk 1a and formed integrally with the stationary disk 1a. The revolving scroll plate 2 has a revolving disk 2a, a scroll wrap 2b protruding from the upper surface of the revolving disk 2a and formed integrally with the revolving disk 2a, and a pin 2c projecting downward from the center of the lower surface of the revolving disk 2a. The stationary scroll plate 1 and the revolving scroll plate 2 are combined so that the scroll wraps 1c and 2b engage.
When the stationary scroll plate 1 and the revolving scroll plate 2 are thus combined, a first compression chamber, i.e., an innermost compression chamber, a second compression chamber on the outside of the first compression chamber, and a third compression chamber on the outside of the second compression chamber, i.e., an outermost compression chamber, are formed between the scroll wraps 1c and 2b. The revolving scroll plate 2 is supported by an Oldham ring 5 on a main frame 6. The main frame 6 is disposed fixedly in an upper portion of the internal space of the closed vessel 10 at a position under the revolving scroll plate 2. A secondary frame 9 is disposed fixedly in a lower portion of the internal space of the closed vessel 10. A crankshaft 4 is supported for rotation in bearings 31 and 32 on the main frame 6 and the secondary frame 9.
A hole 4a is formed in the upper end of the crankshaft 4. The hole 4a is eccentric with respect to the axis of the crankshaft 4. The pin 2c of the revolving scroll plate 2 is fitted in the hole 4a.
An axial lubricating oil hole 4b is formed through the crankshaft 4 along the axis of the same. The lubricating oil hole 4b an upper end opening into the hole 4a and a lower end opening into lubricating oil 13 contained in the bottom of the closed vessel 10.
The crankshaft 4 is driven for rotation by an electric motor having a stator 7 and a rotor 8 fastened to the crankshaft 4 by shrink fit.
An inlet pipe 11 is connected to a lower portion of the circumferential wall of the closed vessel 10 to supply a refrigerant from an external refrigeration cycle into the low-pressure chamber VL. A delivery pipe 12 is connected to the top cover of the closed vessel 10 to deliver the compressed refrigerant gas from the high-pressure chamber VH.
The stationary scroll plate 1 of the prior art scroll compressor thus constructed is provided with a delivery reed valve having a discharge valve element 25 for closing or opening a discharge port 28 formed in the central portion of the stationary disk 1a. The discharge port 28 opens into a recess 24 formed in the central portion of the upper surface of the stationary disk 1a of the stationary scroll plate 1. The discharge valve element 25 is received in the recess 24. The bottom surface of the recess 24 is inclined at a predetermined angle to form a valve element seating surface 27 on which the discharge valve element of the reed delivery valve is seated. The lift of the discharge valve element 25 is limited by a valve holding member 26. The valve holding member 26 is fastened to the valve element seating surface 27 together with the discharge valve element 25.
When the crankshaft 4 is driven for rotation by the electric motor, the torque of the crankshaft 4 is transmitted to the revolving scroll plate 2 to revolve the revolving scroll plate 2 along a circular path by the agency of the Oldham ring 5. Consequently, the volume of the space formed between the scroll wrap 1c of the stationary scroll plate 1 and the scroll wrap 2b of the revolving scroll plate 2 varies to compress the refrigerant. The refrigerant delivered from the external refrigeration cycle flows through the inlet pipe 11 into the closed vessel 10, and then the refrigerant is compressed sequentially in the compression chambers formed between the scroll wrap 1c of the stationary scroll plate 1 and the scroll wrap 2b of the revolving scroll plate 2.
When the refrigerant is compressed by the compressing action to a pressure higher than a pressure on the high-pressure side of the external refrigeration cycle, the the discharge valve element 25 is lifted up by the pressure of the refrigerant and the compressed refrigerant flows through the discharge port 28 into the high-pressure chamber VH. All the refrigerant sucked into the compression chambers is not discharged from the compression chambers and part of the refrigerant sucked into the compression chambers remains in the compression chambers because the delivery valve closes upon the equilibration of the pressure of the refrigerant in the compression chamber and the pressure of the same on the high-pressure side of the external refrigeration cycle. The refrigerant thus discharged into the high-pressure chamber VH of the closed vessel 10 flows through the delivery pipe 12 to the external refrigeration cycle.
The sum of the volume of the first compression chamber, i.e., the innermost compression chamber, immediately before the communication of the first compression chamber and the adjacent second compression chamber and the volume of the discharge port 28 is designated as top clearance. The top clearance must be small to reduce reexpansion loss that occurs immediately after the communication of the first compression chamber with the second compression chamber. The volume of the discharge port 28 which does not contribute to compression must be reduced to the least possible extent to reduce the reexpansion loss. In this specification, the only volume of the discharge port 28 will be referred to as top clearance. The recess 24 is formed in the central portion of the upper surface of the stationary disk 1a to reduce the top clearance. The recess 24 must have a considerably large sectional area corresponding to that of the discharge valve element 25.
Since the prior art scroll compressor is thus constructed, the top clearance of the discharge port 28 needs to be reduced by increasing the depth of the recess 24 to reduce recompression loss in the discharge cycle. However, increase in the depth of the recess 24 reduces the strength and rigidity of the stationary disk 1a. Therefore, there is a limit to the reduction of the top clearance by increasing the depth of the recess 24.
Furthermore, since the recess 24 having the valve element seating surface 27 inclined at a predetermined angle has a complicated shape, it is difficult to machine the stationary disk 1a with an end mill to form the recess 24 and hence the machining cost increases.